Martensitic Stainless Steel: Definition, Composition, Types, Properties, and Applications
Martensitic stainless steel (MSS) is known for its hardness, as well as its poor weldability. Like other stainless steels, MSS has good corrosion resistance and strength when compared to other metals such as aluminum. Its hardness, weldability, and strength can be modified by either slightly changing the composition of the metal or heat treatment.
This article details martensitic stainless steel’s composition, properties, and applications.
What Is Martensitic Stainless Steel?
Martensitic stainless steel is one of five different types of stainless steel. It differs from other stainless steels due to its composition. Its composition allows it to harden and strengthen through heating and aging. Like other stainless steels, martensitic stainless steel is made up mostly of iron with the addition of carbon and other alloys. Carbon makes up around 1.2% of martensitic stainless steel. The other alloying elements are chromium (between 11.5–18%) and nickel. The high carbon content makes martensitic stainless steel strong, but the lack of significant nickel reduces its corrosion resistance.
What Is the History of Martensitic Stainless Steel?
The first martensitic stainless steel was invented by Harry Brearley in 1913. This was the first ever “rustless steel”. The martensitic steel invented by Bearley took until the 1930s/1940s to be commercially produced and used.
What Is the Other Term for Martensitic Stainless Steel?
Martensitic stainless steel is referred to as “martensite”. Other names of martensitic stainless steel include martensite steel and the acronym “MSS”.
What Is Martensitic Stainless Steel Made Of?
Martensitic stainless steel is mostly made of iron with the addition of carbon. Carbon levels for martensitic steel are around 1.2%. Martensitic steel also has 11.5–18% chromium, and a small amount of nickel, manganese, and molybdenum.
How Is Martensitic Stainless Steel Processed?
Martensitic steel is made through the use of quenching and stress relief, or through quenching and tempering. These heat treatments alter the microstructure of the steel to a martensitic structure. This process increases the hardness of the steel.
What Are the Characteristics of Martensitic Stainless Steel?
Martensitic stainless steel is known for its characteristics, such as:
- Corrosion resistance.
- Strength.
- Poor weldability.
- Magnetic in both hardened and annealed conditions.
- Poor formability.
What Is the Color of Martensitic Stainless Steel?
Martensitic stainless steel is silver/gray in color and appears to look the same as many other steels. Additionally, this steel may turn orange/brown when it rusts. The steel may also appear differently when painted.
What Does Martensitic Stainless Steel Look Like?
Martensitic stainless steel appears silver or gray in color, but may also be orange/brown due to rust or another color due to paint. If the martensitic steel is not painted, it may be reflective or matt depending on the surface finish of the material. Figure 1 below is an example of a martensitic stainless steel test specimen:
Martensitic stainless steel specimen for testing.
Image Credit: Shutterstock.com/Digital signal
What Are the Properties of Martensitic Stainless Steel?
Martensitic stainless steel is often referred to as semi-stainless steel as it has a similar composition with a lower alloy content and a higher carbon content. This gives martensitic stainless steel some properties that set it apart from regular stainless steel. These properties are:
- High hardness: MSS's high carbon content compared to other stainless steel gives it a higher hardness.
- Brittle: Conversely, the high carbon content of MSS also leads to a high brittleness.
- Moderate corrosion resistance: MSS had a lower chromium content than other stainless steels which reduces MSS's corrosion resistance.
- High tensile strength: The high carbon content of MSS allows it to respond well to hardening and tempering. This can improve the tensile strength of MSS compared to other stainless steels.
What Are the Physical Properties of Martensitic Stainless Steel?
Table 1 below shows the physical properties of martensitic stainless steel:
| Property | Description | Typical Value Range | Units |
|---|---|---|---|
Property Tensile Strength | Description Tensile strength is the ability of a material to resist plastic deformation when under load. | Typical Value Range 70,000–286,000 | Units psi |
Property Hardness | Description Hardness is the measure of resistance to localized plastic deformation | Typical Value Range ~97 | Units Rockwell B |
Property Density | Description Density is the weight of a material per unit of volume | Typical Value Range 7,800 | Units kg/m^3 |
| Martensitic Stainless Steel Type | Corrosion Resistance | Oxidation resistance | Reactivity | Magnetic properties | Flammability |
|---|---|---|---|---|---|
Martensitic Stainless Steel Type 410 | Corrosion Resistance Lowest resistance | Oxidation resistance Moderate | Reactivity Low | Magnetic properties Ferromagnetic | Flammability Nonflammable |
Martensitic Stainless Steel Type 440 | Corrosion Resistance More resistant than 420 | Oxidation resistance Moderate | Reactivity Low | Magnetic properties Ferromagnetic | Flammability Nonflammable |
Martensitic Stainless Steel Type 420 | Corrosion Resistance More resistant than 410 | Oxidation resistance Moderate | Reactivity Low | Magnetic properties Ferromagnetic | Flammability Nonflammable |
What Are the Different Types of Martensitic Stainless Steel?
Martensitic stainless steel is distinct from other steels due to its composition. However, it can also be further divided into different grades. These grades and their properties are discussed below:
1. 410 Stainless Steel
410 stainless steel is the most common form of martensitic stainless steel and is known as general-purpose martensitic steel. It is often found in the annealed condition and has a minimum tensile strength of 110,000 psi. The hardness value can vary depending on the heat treatments applied. 410 stainless steel is used for fasteners, including nuts and bolts, as well as, valves, pistons, ball bearings, impellers, turbine blades, springs, pins, and micrometers.
2. 440 Stainless Steel
440 stainless steel has the highest hardness when compared to 410 and 420 steel. However, that comes at the cost of reduced formability. This high hardness is sought after for blade manufacturing, as it results in a blade staying sharper for longer. 440 steel is used as blades, in cutlery, surgical instruments, and bearings.
3. 420 Stainless Steel
420 stainless steel is a low-carbon stainless steel, which can have a range of hardness values depending on its heat treatment. When heat-treated and cold-rolled, 420 stainless steel can be expected to achieve a minimum tensile strength of 120,000 psi. 420 steel has applications in fasteners, machine parts, surgical instruments, and firearms.
4. High-Carbon Martensitic Steel
The percentage of carbon in high-carbon martensitic stainless steel is between 0.61% and 1.50% The high carbon content of steel makes it stronger by affecting the molecular bonds between the microstructure. The downside of having a high carbon content is that it makes the steel more brittle and reduces its ability to be welded and formed. Due to its high hardness and strength, high-carbon steel is used for knives, ball bearings, molds, and dies.
5. Low-Carbon Martensitic Steel
The carbon composition of low-carbon martensitic stainless steel is 0.05–0.25%. Having a reduced carbon content allows martensitic steel to be more easily formed and welded, but reduces its strength. Low-carbon martensitic stainless steel generally also has better corrosion resistance and weldability. Due to these characteristics, low-carbon martensitic stainless steel is used in gas & oil pipelines in which a trade-off between strength, corrosion resistance, and weldability is required.
What Are the Applications of Martensitic Stainless Steel?
Martensitic stainless steels have different compositions and different heat treatments available. This results in having a range of strength, hardness, and corrosion resistance. These varying properties allow martensitic stainless steel to be used in a range of applications including:
- Surgical instruments
- Turbine blades
- Fasteners
- Bearings
- Bushings
- Valves
- Micrometers
Is Martensitic Stainless Steel Important in Welding?
Martensitic stainless steel is not known for its use in welding. In fact, it is famously hard to weld. This is because martensitic steel has a tendency to harden, especially when heated and air-cooled or quenched. This reaction to heat treatment leads to the worst weldability when compared to other stainless steels. Martensitic stainless steel’s high hardness and low thermal conductivity lead to weld cold cracking and weld embrittlement.
What Are the Benefits of Martensitic Stainless Steel?
Martensitic steel’s advantages are listed below:
- Low cost.
- Ultra-high strength.
- Moderate corrosion resistance.
- Air hardens.
- Homogeneous weld HAZ/base metal after solution heat treatment.
What Are the Limitations of Martensitic Stainless Steel?
Martensitic stainless steel does have its limitations, one of which is that it is difficult to weld. Additional limitations of martensitic steel are:
- Limited corrosion resistance.
- Susceptibility to cracking.
- Hard to form.
- Limited operating temperature due to a lack of oxidation resistance.
How Does Martensitic Stainless Steel Differ From Regular Stainless Steel?
Martensitic stainless steel has superior strength, hardness, and impact resistance compared to other stainless steel. However, martensitic steel has lower levels of corrosion resistance and magnetism and has very poor weldability. To learn more, see our guide on Stainless Steel Characterisitics.
Is Martensitic Stainless Steel Durable?
Yes, martensitic stainless steel is durable. Martensitic stainless steel responds well to heat treatment by hardening. Its hardened state makes martensitic steel durable for use in applications including: valves, turbine blades, and surgical instruments.
Is Martensitic Stainless Steel Magnetic?
Yes, martensitic stainless steel is magnetic. It is the presence of iron that makes a material ferromagnetic. Since all steels are made primarily of iron, they are mostly magnetic. To learn more, see our Brittle guide.
Is Martensitic Stainless Steel Rust-Proof?
No, martensitic stainless steel is not rust-proof; however, it is rust-resistant. The term “rust-proof” suggests that the material is immune to rust. While martensitic steel, as with other stainless steels, does have increased corrosion resistance, it is not rust-proof. Additionally, when compared to other stainless steels, martensitic stainless steel is only moderately corrosion resistant. This is because martensitic stainless steel's primary sought-after property is hardness.
Can Martensitic Stainless Steel Be Hardened?
Yes, martensitic stainless steel can be hardened. While untreated martensitic steel is known for its hardness, it can also be hardened through the use of heat treatment. Martensitic stainless steel is treated by either heating the metal and then air cooling it or quenching it.
Can Martensitic Stainless Steel Be Tempered?
Yes, martensitic stainless steel can be tempered. While martensitic stainless steel is very hard, this hardness comes with increased brittleness. Since this makes martensitic steel too brittle for many applications, it can be tempered to reduce the hardness and brittleness. This is done by heating the martensitic stainless steel to 135 ºC–400 ºC for several hours.
What Is the Difference Between Martensitic Stainless Steel and Austenitic Stainless Steel?
The difference between martensitic stainless steel and austenite steel is in their weldability. Austenite is much easier to weld compared to martensitic stainless steel. This is because most grades of martensitic stainless steel have a higher carbon content than austenite. The high carbon content also reduces corrosion resistance but increases hardness. Although both materials are different, most martensitic stainless steels are made by heating and rapidly cooling austenite. To learn more, see our guide on Austenitic Stainless Steel.
Summary
This article presented martensitic stainless steel, explained it, and discussed its composition and types. To learn more about martensitic stainless steel, contact a Xometry representative.
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